Clinical evidence has demonstrated that hearing loss during infancy and childhood significantly increases the probability of language and learning disabilities. Experimental evidence suggests that such communicative disorders are augmented by changes in the anatomy and function of the auditory system, changes which are induced by reduced acoustic experience during development. However, interpretation of auditory deprivation experiments has been hampered by inconsistencies in the level of deprivation applied during development by various investigators, as well as by technical difficulties in reversing acoustic deprivation after development. It is the objective of the proposed research to develop a reproducible model of profound acoustic deprivation, and to utilize the resulting procedures to investigate the anatomical and physiological mechanisms by which acoustic deprivation operates. Gerbils and cats will be reared under conditions of extreme acoustic deprivation: the rearing environment will provide greater than 80 dB of isolation from external auditory stimuli; noise within the rearing environment will be minimized; and the auditory system will be surgically isolated from ambient stimuli by 50-60 dB. The effects of deprivation upon synaptogenesis and neuroanatomy will be examined at the ultrastructural level in the cochlea, VIIIth nerve and cochlear nucleus. Effects upon auditory function will be examined electrophysiologically at the same locations. Effects of acoustic deprivation procedures upon the external and middle ear will be bypassed by mechanically displacing the stapes in all measures of auditory function. In a companion study, the minimum acoustic stimulation necessary to maintain normal auditory development will be investigated.